One of the problems to be overcome in the design and operation of high pressure, hydraulic gear pumps is that of counterbalancing the axial and radial force components imposed on the meshed gears and their support structures due to the high pressure developed at the discharge side of the pump when the latter is in operation. Such forces tend to shift the gears and their supports toward the low pressure or inlet side of the housing. In addition, the high pressure forces tend to cause the plates or bushings which support the gear shafts to become cocked in the housing with a resulting loss in pumping efficiency, increased power requirements and excessive wear.
One solution to the aforementioned problem is disclosed in my prior U.S. Pat. No. 2,772,638. The gear pump or motor disclosed in this patent utilizes an internal unit assembly construction wherein the liquid displacing elements or gears, and the structure for supporting the gears in meshed, operating relation, are removable as a unit from the housing of the device. The internal unit assembly includes axial pressure loading chambers, which maintain a pumping seal between the side faces of the gears and supporting end plates of the assembly, the reaction forces from the axial pressure loading chambers being taken up by the gear shafts. Because of the fact that the forces which maintain a running seal between the side faces of the gears and the end plates are confined to the components of the internal unit assembly, the housing for the pump is not subjected to large forces and hence does not have to be of a high structural strength. Moreover, the internal unit assembly can be readily removed as a unit for purposes of inspection, repair or replacement, as need be.
In my prior U.S. Pat. No. 3,029,739, an hydraulic pump or motor is disclosed and claimed which likewise utilizes an internal unit assembly type construction. The internal unit assembly disclosed in U.S. Pat. No. 3,029,739 also employs one or more axial pressure loading chambers for maintaining a seal between the side faces of the meshed gears and the end plates which support the same. In addition, one or more radial pressure balancing chambers are defined between the internal unit assembly and housing for counterbalancing the radial force component developed at the discharge side of the internal unit assembly when the pump is in operation so that the internal unit assembly is maintained in a prescribed reference position in the housing. Efficiency is thus maintained throughout the operating speed and pressure ranges of the pump.